Improvement of flavonoid aglycone and biological activity of mulberry leaves by solid-state fermentation

Mulberry leaves contain various types of phenolics, especially glycosides of the flavonoids quercetin and kaempferol. The aim of the present study was to investigate the production of quercetin and kaempferol as well as the biological activity of mulberry leaves with solid-state fermentation by edible fungi. Among the test fungi, the fermentation with Monascus anka was found to obviously increase the level of quercetin and kaempferol in the mulberry leaves. After fermentation, the amounts of quercetin and kaempferol were up to 5.30 +/- 0.35 mg/g dw and 1.87 +/- 0.10 mg/dw, respectively. Meanwhile, the changes in enzymes activities and the contents of quercetin and kaempferol during fermentation were systematically studied. The morphology observation demonstrated that the mulberry leaves were severely damaged after fermentation. In addition, the biological activities including free radical scavenging activity, a-glucosidase inhibition activity, and antimicrobial activity significantly enhanced with fermentation. This study provided a scientific basis for the production of the high value flavonoid aglycones from plant materials.